colesulen.

/ˈkɒlɪsjuːl/Etymology: < modern Latin colesula, irregular diminutive of Greek κολεός sheath.
Botany.
1882 B. Carrington in XIV. 718 On section of the colesule a number of minute..bodies are found.
This entry has not yet been fully updated (first published 1891; most recently modified version published online June 2018).